The present invention relates to an arctic benchmark and more particularly relates to a method and apparatus for installing a benchmark in an arctic region wherein the benchmark provides a highly accurate, reliable position and elevation reference mark even after prolonged exposure to arctic conditions.
As is well known, "benchmarks" are reference points of known elevation and position which are used in surveying operations. Some benchmarks are merely marks on permanent-type structures or landmarks, e.g. buildings, walls, trees, etc. while others e.g. markers or monuments such as stakes, concrete blocks, have to be installed at known positions and elevations. The latter benchmarks are usually driven or otherwise set in the ground to a depth at which their positions and elevations will not be changed or disturbed by normal surface conditions.
However, in arctic regions, due to the natural composition of the arctic land surfaces, problems arise in providing benchmarks which are reliable over prolonged periods of time. As shown, the permafrost layer which covers most land areas in the arctic regions has an "active layer" extending from the surface to a depth of approximately six feet. This active area undergoes partial thawing during "summer" months and refreezing in "winter" months. When a benchmark is set into or through this active area, the changing conditions thereof can cause shifting or subsidence of the benchmark which, in turn, leads to inaccurate readings (especially elevational readings) during subsequent survey operations. Although the inaccuracies in the readings may be small, they are of great concern whenever the readings from the benchmarks are relied upon to determine when and if a particular piling, building or other structure is subsiding and to what extent.